Method of forming reflecting surfaces



' May 4, 1926. 1,583,268

B. BART METHOD OF FORMING REFLECTING SURFACES Filed June 10, 1920 Patented May 4, 1926.

UNITED STATES PATENT. oFFicE;

BLASIUS BART, OF NEWARK, NEW JERSEY.

ITETHOD OI FORMING REILECTING SURFACES.

Application filed June 10,

reflecting light such as metallic silver on an ob'ect to be coated and the invention speci cally relates to an improvement in the process of forming metallic silver reflectors.

It is the general practice in the art to which this invention relates to mix a solution of a silver salt, such as silver nitrate, with a reducing agent, such as Rochelle salt, and to flow the mixture over the object to be coated. This old method with the re- 1 agents in liquid bulk is wasteful in the amount of reagents used, provides coatings of unequal thickness, forms part of the layer-of a different character from an adjacent part such as the formation of nonreflecting minute particles and is otherwise objectionable, particularly when attempts have been made to practice the same on a large commercial scale.

The primary object of the present invention is to attain a brilliant reflecting surface of uniform high lustre, simulating a highl y polished silver surface and to attain this result with minimum loss of reagents, rapidly and in a manner susceptible of adoption for use on a large commercial scale and capable of being operated successfully by unskilled labor.

To attain this object I cause the reagents each to assume the form of a nebulous cloud of spaced apart, very fine particles, which floating particles will be caused to react chemically preferably but not necessarily while in the air and the metallic silver so formed is coevally deposited on the surface.

progress of the depositing steps of the process. This feature of the invention practiced by initially causing the particles in 1020. 'Serial no. 381,974.

the silver precipitating cloud to have a relatively larger percentage of silver present than would be indicated'bythe theoretically correct amount required by chemical calculation to effect the reducing action.

This preponderance ofsilv'er forms an. ex v tremely brilliant surface layer and for re'a-' v sons of economy in the use of silver is made extremely fine,

in fact with no {perceptible thickness. The proportion of silver solu tion to its reduclng reagentis then caused 5 to approach the true theoretical chemical reacting proportions, that is, in theillustration above referred to, the silver ispresent in a proportion of about one-third ofthe Rochelle salts solution present. It will be understood, however, that these proportions are merely suggestive of the particular example seleeted for illustration-and obviously will vary under the conditionsfcontrolling processes of the type underdiscuss'iont.

Another object of the invention is top' ro e vide a process which can be practiced more rapidly than can be eflected with themethods now in general use, at the same time' to feature economy in the use of-the reagents and to attain asensitive control over the character of the coating being formed.

\ I attain this object byobserving certain refinements of procedure, such for instance,

as the concentration of the solutions usually en1ployed,'the heating of the mould or object to be coated, the cautious directing of the precipitating cloud uniformly over the surface to be coated and the insuring of the completely formed initial layer of the coating before changing the proportions of the reagent for the succeeding layers.

In this disclosure reference is made to layers, but it is appreciated that there is-but one integral coating which in the case of the reflectors selected for illustrationis not more than one-twenty-fifth of a millimeter.

Various other objects and advantages of the invention will be inpart obvious from the suggestions herein made relative to the w improved process and from an inspection of the accompanying drawings showing the prec pitatmg cloud, and in part Wlll be more fully set forth in the following particular description of one practical method of practicing-the invention and the invention also cons sts in certain new and novel combinaftion of steps hereinafter set forth and claimed.

Referring to the accompanying drawings,

there is shown largely in diagrammatic outline a suggested form of apparatus for practicing the process featured in this disclosure.

In the drawings there is shown a convex,

I chemically clean and preferably highly pol thin silver coating thereon is positioned in an electrolytic vat and a deposit of a strengthening material, such as copper, is formed on the rear side thereof, after which the copper backed silver coating is removed from the depositing vat.

In the drawings there is shown an atomiziug tool 11 but it is to be understood that the tool illustrated is illustrated and hereinafter described simply to show a form of apparatus by means of which the method in one aspect of the same may be racticcd; The tool is provided with some orm of handle 12. The tool illustrated is of the four jet type selected in order to disclose the use of an additional reagent in the process, hereinafter more fully disclosed, but in general practice the tool will be equipped simply with three nozzles 12, 13 and 14 replaceable with nozzles having different discharge vents thereby to change the proportion of the reagents discharged per unit of time. The nozzle 12 communicates through a pipe connection 15 with a source of supply of a silver solution, herein indicated symbolically by a tank 16. Similarly the nozzle 13 is connectcd by means of a pipe connection 17 to a source of supply of a reducing agent, indie cated symbolically by a tank 18. For the purpose of this disclosure it will be considered that there is present a solution of silver nitrate in the tank 16 and a solution of tartaric acid in the tank 18.

The nozzle 14 connects by means of a pipe 19 with a source of compressed gas, herein suggested as air, and represented by a compressed air tank 20.

The air nozzle discharge nozzle 14 defines the axis of the silver precipitating cloud 21 and the discharge vents 22 and 23 of the nozzles 12 and 13 respectively are extremely fine in discharging cross-section and discharge their contents one slightly in advance of the other and .both at right angles to the direction of the air stream discharged from the nozzle 14.

The tanks 16 and 18 are provided, respectively, with main control valves 24 and 25 but the rate of discharge from the nozzles will depend primarily upon the flow coated.

discharging capacity ofthe vents 22 and 23. In the device selected for illustration it is intended that the reducing agent be supplied in an amount three times greater than the amount of silver solution supplied per unit of time, and accordingly the vents 22 and 23 are cautiously designed to give this proportional rate of discharge.

- \Vith the parts in the position illustrated in the drawings the valve.25 is shut oil slightly so as to give a slight reponderance of silver discharged compareil to the theoretically defined amount of reducing agent as usually practiced in the flow method now in general use. lVith this slightly strong silver solution discharging in the form of fine mist rather than a rain of drops into the similar cloud of reducing reagent the tool is moved about. until all parts of the surface of the mould is uniformly but slightly After the initial coating is formed the valve 25 is full opened and the operation is continued, t 1e operator passing back and forth and across the mould until the desired thickness of silver coating is attained.

The best results are attained when the mould is heated and while any temperature above room temperature is suggested, a temperature of 90 F. has been found to be most effective in forming devices of the type herein particularly described.

l/Vhile the invention, as thus far described, is complete in itself, it is herein suggested that under some circumstances ammonium hydroxide may be added to the precipitating cloud. It is appreciated that any excess of ammonium hydroxide in the reaction, above outlined, would spoil the same, but addition of a very small amount of ammonium hydroxide is practiced with advantage when the mold is cold and has the effect of acting as a speeding reagent.

For this purpose there is disclosed in the drawings, an additional nozzle 26 which leads by means of a pipe'27 to a source of supply of ammonium hydroxide indicated by the tank 28. The nozzle 26 is provided with an extremely fine discharge vent 2.9 which points in the same direction as the vents 22 and 23 and adds a small spray of ammonium hydroxide to the reagents discharged by the vents 22 and 23.

It has been found upon analyzing the byproducts flowing off the coated mould that there is very little silver present. As tartaric acid and ammonium mtrate is relatively cheap the process features economy in the use of the expensive silver material. Further featuring economy, it is possible by practicing the method disclosed toefi'ect an intensely brilliant but very thin coating to theface of the'fo-rmcd reflector and to back the extremely brilliant face with a very thin layer of silver which is not quite so brilliant. This before an abnormally thick 10 part an geases I additional thickness is necessary in order to revent dissolving in thesubsequent electroytic bath treatment but thecoating can be made of uniform thickness, a resu t which is possible due to the fact that as a very small amount of the coatingl is deposited at any one time the operator nity to move the tool over another portion layer can form.- It is understood that .the operator comes back re eatedly' over a previously coated cl in this way attains accurate control over the forming layer and with a little experience can readily gauge the thickness desired on the different parts of the coating. .The practicing of the process with the use of silver has been featured in this disclosure due largely to the fact that applicants efforts have been connected with the development of silvered reflectors, but it is appreciated that the process is equally apclaim plicable, in the case of reflectors, to other ght reflecting metals for instance platinum' and gold and these metals are to be considered as the chemical equivalent of the silver recited in the following claims whenever such subsitution of metals is permissible.

. Certain other metals, such as nickel and .co

balt have been tried but do not give the satisfactory results'above recited for silver. It is further suggested thatthe process can be practiced with certain alloys and metal mixtures and as one such mlxture a comblnedgold-silver deposit has given a most beautiful'refiecting surface.

Having thus described my invention, I

1. In the 'art of coating objects with a silver deposit, the process which consists in formin a cloud-like mist of small particles of a silver compound diflused into a similar cloud'of small particles of a compound designed to react chemically on the silver compound to precipitate fine metallic silver and permitting the metallic silver particles so formed to deposit on the object to be coated.

2. In the art of coating objects with a silver deposit, the process which consists in intimately mixing a cloud of small, se arated particles of a silver compound wlth a cloud of small particles of a substance capable of reacting with the silver compound particles to form fine particles of metallic silver and causing themetallic silver particles so formed to collect immediately on the object to be coated.

8. In the art of coating objects-with a silver deposit, the'process which consists in intimately mixing in air a cloud of small, separated particles of a silver solution, associated with said silver particles a cloud of particles of an agent capable of reducing the silver compound, said reducing agent being in close physical contact with the particles as an opportucles of the silver solution and reducin 'agent.

to react chemically while passing through the air and immediately receiving the re-- sulting metallic silver particles on the object to be coated. -4. In the art of coating objects with a silver deposit, the processwhich consists in intimately mixing while in the air a cloud of'small, separated particles of a silver solution, a'cloud of particles of an agent capable of reducing the silver compound to form metallic silver, said reducing agent while passing through the air being in close physical contact with the particles of the silver compound, causing said particles to react chemically While passing through the-air and receiving the resulting metallievsilver particles on the object to be coated while permitting the hy-products formed to flow off the coated surface and thus leave the object coated with fine silver particles.

"5. Inthe art of coating objects-with a silver deposit, the process which consists in, forming a cloud of fine particles comprising a silver compound and a. reducing agent with the particles of the former present in a proportion of about one-third of. the

action betWeen theparticles of the silver compound and the reducing agent andreceivingthe formed metallic silver particles onthe object to be coated at the termination of the passage of the particles through'the air. '1

6. In the art of coating objects with a silver deposit, the process which consists in forming a cloud of fine particles. comprising a silver compound and a reducing agent with the particles of the former.- present ina proportion of about one-third of the particles of the reducing agent and causing said cloud to pass through space for a relatively short distance to permit a brief reaction between the particles of the silver compound and the reducing agent, receiving the formed metallic silver particles on the object "tobe coated at the termination of the passagebf the particles through the air and causing a spray of a speeding reagent to commingle with the cloud.

-7. In the art of coating objects with a silver deposit,- the process which consists in forming in air a cloud of fine particles comprising a silver compound and a reducing agent, in which the silver-compound is presthrough the air for a relatively short distance to permit a brief reaction between the particles of the silver compound and the re'-.- ,ducing agent and receiving the formed metallic silver particles on the (object to bespraying on the object a mist of a silver solution and a reducing agent, causingthe reducing agent to react on the silver as the mist is depositedthereby toform a brilliant face layer to thecoating and then reducing the percentage of the silver constituent in the spray until the proportion ofsilver to its reducing agent is approximately one to three thereby to form less brilliant portions to the part of the coating back of the face layer. 7 I a I I 9. In the art of coating objects with'metallic silver, the process which consists in causing a mist of fine .particlesof silver nitrate, tartaric acid and ammonium hydroxide to commingle in space and to fall on the object. r l

10. In the art. of coating objects with metallic silver, the. process which consists in causing a mist of fine particlesof silver nitrate and tartaric acid to comminglein space and to fall on the object.

11. In the art of coating an object with silver, the process which consists-in heating the object and while the object has a temperature greater than room temperature, causing a cloud of metallic silver particles to be formed in close proximity to the surface of the object to be coated and immediately ermitting the freshly formed silver partic es to fal gently as a cloud or mist onto said heated surface.

12. In the art of coating an object with silver, the process which consists in causing a cloud of finely divided particles of silver nitrateto mix with a cloud of a silver nitrate reducing agent in which mixture the silve'r is present in an amount approximately onethird of the amount of the reducing agent present and causing said cloud mixture to lay on the object to be coated.

13. In the art 'ofcoating an object. with silver, the process which consists in causing a cloud of finely divided particles of silver 7 nitrate to mix with a cloud of a silver. nitrate 'on the object to be coated.

14. In the art of coating objects with metallic silver, the process which consists in forming metallic silver in such extremely fine articles that they will lazily float d'ownwar ly in air and immediately receiving the nascently formed silver particles on the surface to be coated.

15. In the art of coating the surface of an object with silver the process which consists in causing a clou of finely divided particles of silver nitrate to mix with a cloud of a silver nitrate reducing agent in which mixture the silver 15 resentin an amount a proximately one-t lild of the amount of t is reducmg agent present causing the cloud mixture to contact with the surface, said surface having a temperature greater than the temperature of the depositing silver particles.

16. In the art of preparing a coating for covering an object with silver, the process resent, said reducing reaction taking place in the resence of ammonium hydroxide.

17. n the art of coating objects with a light reflecting metal, the process which consists in forming the metal into a nebulous cloud of finely divided spaced a art particles, subjecting this metallic clou' to a similar cloud of a reagent capable of reacting chemically while in the air to. reduce the metal in the cloud and causing the reduced metal promptly to lay on the article to be coated.

Signedat New York city, in the county of New York and State of New York, thisfith day of June, A. D. 1920.

BLASIUS BART. 

